Collisionless and collisional (self-quenching) rate constants were measured for several rotational states of the V 2 1 K 0 1 and V 2 1 K 2 1 subbands of acetylene under bulk conditions. For jet-cooled acetylene, the collisionless decay rates measured for the 1 1 6 1 V 1 6 K 1 0 subband are larger than those for the V 2 1 K 0 1 and V 2 1 K 2 1 subbands. The present results are compared with the kinetic data available from the literature. The differences observed among the collisionless rate constants as a function of vibro-rotational energy are explained in terms of non-radiative processes in acetylene.